Effect of varying the concentrations of PF4 and heparin on the induction of TF expression in PBMCs. (A) Increasing amounts of heparin were added to PBMCs containing 100 μg/mL KKO and 10 μg of PF4. Samples were incubated for 6 hours at 37°C, and TF activity was measured with a one-stage clotting assay. (B) Increasing amounts of PF4 were added to PBMCs containing 100 μg/mL KKO and 1 U/mL heparin. TF activity was measured with a one-stage clotting assay. Results are from 3 independent experiments.